Electrical insulator



p i 1966 E. G. DORGELO 3,247,313

ELECTRICAL INSULATOR Original Filed June 7, 1962 LOSSES WA 7715 WA 7 T5COOL //V6 TEMPERATURE TfMPEPATl/AE INVENTOR. ED014120 G. Dozeano m Alf;

AGEN.

United States Patent 3,247,313 ELECTRICAL INSULATOR Eduard G. Dorgelo,Huntington, Long Island, N.Y., assignoi' to North American PhilipsCompany, Inc.,

3,247,313 Patented Apr. 19, 1966 ICC envelope, only the base or topportion of the envelope is made of a low-loss glass which is joined to anormal glass used for the remainder of the envelope. The purpose ofusing a low-loss glass of the hard variety, such as an New York, N.Y., acorporatio of D l 5 aluminosilicate glass manufactured by the CorningGlass Continuation of application Ser. No. 115,469, June 7, Company andunder glass e 1723, Is t Such 9 This application 4, 19 329, 03 glasseshave low electrical losses at high frequencies. The 5 Claims. (Cl.174--50.61) remainder of the envelope and of the top may consist of aborosilicate glass also made by the Corning Glass Com- This applicationis a continuation of my application 10 any under the code designated7052 since it is easier to Serial No. 115,496, filed June 7, 1961, nowabandoned. melt in order to form a seal.

My invention relates to electrical apparatus, and more In manufacture ofthe tube, powder particles of the particularly, to ways and means forelectrically insulating special glass are poured into a graphite mold insuch a metal Parts and the like- The invention is of p ifi way that onlya central area is covered, the remaining part terest in the manufactureof electric discharge devices andof th ld th b i fill d ith powder m def o th the like. normal glass. Thereafter, the mold is heated up to atem- In electric discharge tubes particularly adapted to operperature atwhich the special glass has reached the right ate at high frequencies,the field between adjacent viscosity. Before this temperature isreached, the normal mihais may he 80 strong that the glass between theglass had already obtained a more or less liquid state and minalsmelts'due to excessive high frequency losses. This starts to penetrateinto the still unliquified central portion. situation y he iIhPTQVed yUsing a special low-less After cooling down, a glass plate withsealed-in pins is glass to insulate the tehmihaissuch glasses eXist andobtained, the central portion of which consists of a 100% arecommercially available. Unfortunately, most of them l .1 glass hil th if th l t o i t f 100% belong to the g p of y hard glasses Which meansthat normal glass. The intermediate zone in which both glass y hotflames have to he used during the sealing p components are mixedconstitues a kind of circular gradtiOIl- Furthermore, the Viscosity ofthis glass at Wefkihg ed seal, eliminating dangerous thermal stresses.Since temperature will be considerably different from the visthe iconsists only of normal glass, h 1i i eosi'ty of adjacent P and 'theTe ye also a marked tion can be accomplished in the normal routineway.difference in thermal expansion. The invention will be described inconnection with the It is an object of my invention to provide animproved accompanying d i i hi h; means for electrically insulatingmetal parts and the like. FIG, 1- Shows an envelope f l i discharge tubeIt is another object of my invention to seal electrically id d i h 1 d-id t conductive elements in a glass envelope for an electric FIG 2 i vportion f h envelope h i h 1 d i discharge tube adapted to operate atrelatively high freconductors extending h u h a t l quencies. FIG. 3 isa mold for making the top plate of the en- A further object of myinvention is to provide an iml PiOVed and simpler method of sealingelectrically e011- FIGS. 4 and 5 show typical loss and cooling curves ofductive members in a glass envelope in which a special diff t types of llow-loss glass is e p y ihbetweel} e i around the i As shown in FIG. 1,lead-in conductors 1 of an electric trically conductive elements tominimize the electrical 40 discharge tube extends through [the ,baseand/or top of the tlosses 1n the glass and to improve the insulationtherebeenvelope 2 of the tube. Ween The top plate 3 of the envelope, asshown in FIG. 2, These and further (ibiects of my mventlon Wlu beapconsists of two portions 4 and 5 made of different glass. parent asthe speclfiqatlon p i Portion 5, which is intermediate and surrounds thelead-in In accordance with my invention, in order to reduce d 1 d f 11 11 h losses between conductors, for example in an electric dis- Conuctofs 3 i ma e O a Special 055 g sue charge tube the conductors areSurrounded by a glass pop an aluminosilicate glass manufactured by theCorning tion which is easily fusible to the remainder of the en- Companyunfier Code Q' 1723 the PmPemes of velope but between the conductors,the glass has a rewhich e specified 111 the toiiewlhg table- TherrOundduced thickness, or preferably consists of a special type POTtlOn4 of the glass Plate is made of normal glass of glass known as a iowioss glass such as a borosilicate glass manufactured by the CorningSince the lead-in conductors of an electric discharge Glass Companyunder the Code No. 7052. The followtube extend either through the baseor the top of a glass ing table specifies the characteristics of theseglasses:

Viscosity Data 2 Dielectric Properties at 1 Mo Logo of VolumeResistivity 3 Thermal Power Factor 4 Class Code Expansion Coefi./ 0.Strain Anneal- Softening Working Dielectric Point, ing Point, Point,Point, Const.

0 0. 0. 25 0. 250 0. 350 0. Room 200 0.

Temp.

1723 (center) 42 10 670 708 912 1, 17s 13. 5 11. 3 1a 14 6.3 7052 rim)46 10-" 435 480 708 1,115 17 9.2 7.4 26 5.1

1 From 0 to 300 C. in/in C. or cm./cm./ C. 2 These data subject tonormal manufacturing variations.

3 Data at 25 extrapolated from high temperature readings and areapproximate only.

4 Power factor defined as tan 6. Multiply by 10 5 This value measured at25 C.

In the manufacture of the top plate 3 lead-in conductors 1 are placed inapertures in a graphite mold 6 (FIG. 3) and powdered particles of thespecial hard glass are poured in such a way that only the central areaand the area immediately surrounding the pins are covered. The remainingportion is then filled with powder made from normal glass, i.e., aborosilicate glass. Thereafter the mold is heated up to a temperature atwhich the low-loss glass has obtained the correct viscosity, 1l=00 C.Before this temperature is reached, the normal glass has already reacheda more or less liquid state and starts to penetrate into the stillunliquified portion. Upon cooling down the glass plate with sealed-inpins has a graded glass seal, the central portion of which contains 100%low-loss glass. The rim portion can then be sealed in the conventionalmanner to the remainder of the envelope 7.

In certain applications the temperature between adjacent terminals willrise so much that the glass between the terminals melts due to excessiveelectric losses. Whether or not this phenomenon will occur depends uponthe. slope of the losses Versus temperature curve in relation't-o thecooling curve. This is demonstrated in FIGS. 4 and 5. In FIG. 4, thedielectric losses rise rapidly with temperature. Such is the case withglass having a high positive value of the temperature coefiicient of thedielectric loss factor. The power (watts) carried off by cooling isshown to be only slightly dependent on temperature. The point ofintersection in this case is an unstable point and it is clear that anyincrease in temperature above the equilibrium value gives rise toafurther increase. Under these conditions, the glass will melt after ashort time.

In FIG. 5 cooling is improved and at the same time a material with a lowpositive value of the temperature coefiicient of the power factor hasbeen shown. As can easily be seen, the point of intersection nowindicates a stable equilibrimn. It should be noted, however, that in thelatter case, the loss factor itself may be quite high. However, it isimportant that the temperature coeificient of the loss factor of theglass have a low'value.

In principle, the glass between the lead-in conductors may have a higheror lower viscosity than the surrounding glass, the only requirementsbeing that it has a'low temperature coefficient of the loss factor andthat, if the glasses have different coefficients of expansion, excessivethermal stresses be prevented by a graded seal being formed between thetwo types of glass. The invention is primarily concerned with reducingthe losses in the glass between conductors provided by electrical fieldsbetween the conductors. If 'a low-loss glass of reduced thickness isused between the conductors and a normal glass, which is easily fusible,around the conductors, a further improvement can be obtained.Consequently,

- 4 the invention is not limited to the specific glasses describedherein, since other glasses having similar characteristics may be used.

While I have thus described my invention in connection with the specificembodiments thereof, other modifications will be readily apparent tothose skilled in the art without departing from the spirit and scope ofthe invention.

What is claimed is:

1. An envelope for an electric discharge tube having a portion throughwhich electrically conductive elements extend spaced by electricallyinsulating zones, said envelope portion comprising a first part whichextends between and immediately surrounds the conductive elements andconsists of a glass having a power tactor of less than 20 x 10- and asecond part immediately abutting said first part and spaced from saidconductive elements consisting of a glass having a power factorexceeding 20 X 10- said second part having a lower melting point thanthat of the glass of the first part to facilitate sealing thereof toremaining portions of the envelope.

2. An envelope for an electric discharge tube as claimed in claim 1 inwhich the thermal coefiicient of expansion of the glass of the firstpart of approximately 42 x10- and that of the second part approximately46 x 10- 3. An envelope for an electric discharge tube as claimed inclaim 2 in which the glass of the first part is an aluminosilicate glassand that of the second part a borosilicate glass.

4. An envelope for an electric discharge tube as claimed in claim 3 inwhich the thickness of the first part between the conductive elements isless than that of the surrounding glass parts.

5. An envelope for an electric discharge tube as claimed in claim 1 inwhich the temperature coefiicient of the power factor for the glass ofthe first part is substantially smaller than that of the glass of thesecond part.

References Cited by the Examiner UNITED STATES PATENTS 1,830,526 11/1931Boss ard 174-50 X 1,968,854 8/1934 Pirani et al. 313-J2'2l 2,177,72810/1939 Krelft et al. 313-22l X 3,123,470

3/ 1964 De Nison 43

1. AN ENVELOPE FOR AN ELECTRIC DISCHARGE TUBE HAVING A PORTION THROUGHWHICH ELECTRICALLY CONDUCTIVE ELEMENTS EXTEND SPACED BY ELECTRICALLYINSULATING ZONES, SAID ENVELOPE PORTION COMPRISING A FIRST PART WHICHEXTENDS BETWEEN AND IMMEDIATELY SURROUNDS THE CONDUCTIVE ELEMENTS ANDCONSISTS OF A GLASS HAVING A POWER FACTOR OF LESS THAN 20 X 10-4, AND ASECOND PART IMMEDIATELY ABUTTING SAID FIRST PART AND SPACED FROM SAIDCONDUCTIVE ELEMENTS CONSISTING OF A GLASS HAVING A POWER FACTOREXCEEDING 20 X 10-4, SAID SECOND PART HAVING A LOWER MELTING POINT THANTHAT OF THE GLASS OF THE FIRST PART TO FACILITATE SEALING THEREOF TOREMAINING PORTIONS OF THE ENVELOPE.